A fuel pump typically has a housing, a motor received in the housing and an impeller driven by the motor. The impeller is rotated to drive fuel through the housing, and the motor. The motor has a rotor which includes a shaft, a rotor core fitted to the shaft, a commutator fitted to the shaft, and a plurality of windings wound around the rotor core. In order to improve the balance of the rotor, a groove is formed at a radially outermost surface of the rotor core by milling. Due to the characteristics of milling techniques, on one hand, the groove can only be formed on the outermost surface of the rotor core; on the other hand, a radial depth as well as a circumferential width of the groove varies along an axial direction of the rotor core, which causes undesired vortex flow when fuel flows through the motor.
Therefore, there is a need for an improved motor that can overcome the shortcomings described above.